Relationship between Low-frequency Oscillations of Atmospheric Heat Source over the Tibetan Plateau and Longitudinal Oscillations of the South Asia High in the Summer

The NCEP/NCAR reanalysis daily data for the period of 1983-2012 has been exploited to analyze the characteristics of low frequency oscillations of the vertically integrated atmospheric heat source over the Tibetan Plateau (TP) and longitudinal oscillations of the South Asia high (SAH) in the summer. The relationship between them is also discussed. Results indicate that the major low frequency cycle of heat source over eastern TP and the longitudinal displacement of SAH both are about 10-20 d. At the peak phase of the 10-20 d low-frequency heat source oscillation in the eastern plateau in the summer, 10-20 d low-frequency cyclones are dominant over the TP while anticyclones are dominant over the western TP. As a result, the SAH moves westward and appears as Iran high. At the valley phase of the oscillation, the low-frequency synoptic circulation pattern is completely opposite to that at peak phase. TP is under control of low frequency anticyclones while the western TP is controlled by low-frequency cyclones. Under this situation, the SAH moves eastward and appears as the Tibetan High. Wind field variations caused by changes in the warm center above the TP due to the thermal field anomalies can explain the SAH longitudinal oscillation.